High-gain Gaseous photomultipliers for the visible spectral range A. Breskin, A. Lyashenko, R. Chechik Weizmann Institute of Science, Rehovot, Israel J. M. F. dos Santos, F. D. Amaro Univ. of Coimbra, Portugal J. F. C. A. Veloso Univ. of Aveiro, Portugal Talk dedicated to my friend Georges Charpak Celebrating 85 in March 2009 TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
Photomultipliers should go flat! SK F 500 mm Vacuum PMT Gaseous PM ~10 mm Bulky, High cost ~11, 000 PMTs hn readout n-induced m ring Flat, Low cost photocathode Gaseous electron multiplier NEXT: UNO : 56, 650 PMTs Hyper-K: 200, 000 PMTs !!! Super Kamiokande who can pay? TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
UV - Gaseous Photomultipliers (GPM) UV-GPMs used in experiments: ALICE, HADES, COMPASS, J-LAB, PHENIX NEW! Thick-GEM Talk by Chechik CERN-ALICE 400 x 600 mm 2 PHENIX 250 x 250 mm 2 Cs. I photocathode UV photon e. THGEM readout electrode Double-THGEM Wire-chamber GPM Rev: Chechik & Breskin, NIM A 595(2008)116 TIPP 09 Tsukuba Triple-GEM CRYO: Bondar, 2008 JINST 3 P 07001 VISIBLE-SENSITIVE GAS-PMs A. Breskin
Secondary effects in GPMs “open geometry” GPM hn Hole-multiplier E 1 e in drift E GEM hole E PC DV + ++ ind >1000 e out Main problem: Ions & photons secondary e emission Ion & photon feedback pulses gain & performance limitations TIPP 09 Tsukuba PC masked by electrode • Much lower photon feedback • Lower ion-feedback • better performance VISIBLE-SENSITIVE GAS-PMs A. Breskin
Visible-sensitive GPMs Motivation for R&D: GEM: Gas Electron Multiplier Sauli, NIM A 386(1997)531 • large areas • flat geometry (1 bar gas) • operation in magnetic fields • sensitivity to single photons • fast (ns) • high localization accuracy (sub-mm) • low cost (dream: few-$/cm 2) Previous status: 70μm 50μm Sealed Triple-GEM with K-Cs-Sb • bialkali stable under avalanche • gas detectors with coated bialkali • Sealed triple-GEM with bialkali • high gain only inpulsed-gate mode • low aging under avalanche • MAIN DIFFICULTY: ION FEEDBACK Balcerzyk, IEEE Trans. Nucl. Sci. Vol. 50 no. 4 (2003) 847 Rev: Chechik & Breskin NIM A 595 (2008) 116 TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
Visible-sensitive GPM: Ion-feedback development K-Cs-Sb Cs. I K-Cs. Sb, Na-K- b, Cs- : Current S Sb deviates from exponential Max Gain ~ few 100, IBF~10% if stable operation of visible sensitive GPM G~105, γ+eff ? , IBF ? TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
IBF depends on effective ion-induced electron emission from PCs PC backscattering on gas molecules Function of Ee- (~7 e. V) extr ~ 7% in Ar/5%CH 4 Function of: Eion & PC material (Eion~13 e. V for CH 4+) e PC K-Cs-Sb Na-K-Sb Ion CH 4+ 0. 03± 0. 01 0. 02± 0. 006 0. 027 0. 029 γ+eff (experimental) γ+eff (theory) if stable operation of visible sensitive GPM 5 -4 Ar/CH 4 (95/5), γeff+ ~0. 03, Gain ~ 10 IBF < 3. 3*10 Lyashenko et al, in preparation TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
Cascaded-GEM GPMs: high gain but also high ion back-flow Semitransparent GPM 107 105 103 Reflective GPM TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
IBF: Ion Back-Flow Fraction IBF: The fraction of avalanche-generated ions back-flowing to the photocathode IBF @ Edrift 0. 5 k. V/cm, Gain ~105 : Bachman, NIM A 438(1999)376 IBF= 5% Breskin, NIM A 478(2002)225 IBF= 2 -5% Bondar, NIM A 496(2003)325 IBF= 3% IBF~5 10 -2 Need another factor of 100!!! Challenge: BLOCK IONS WITHOUT AFFECTING ELECTRON COLLECTION TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
Gaseous detectors with Visible-PC operated with ion gating Moerman, Ph. D Thesis, 2005 JINST TH 004 Breskin, NIM A 553 (2005) 46 106 NO FEEDBACK ! Ion gating GATED MULTI-GEM DC: IBF~10 -1 → gain limited to 102 Ion gating: IBF~10 -4 → gain ~106 But: gating dead-time; needs trigger TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
The Microhole & Strip plate (MHSP) Two multiplication stages on a single, double-sided, foil Strips: multiply charges -2 IBF ~ 10 MHSP: Veloso, Rev. Sci. Inst. A 71 (2000) 237 Maia, NIM A A 523(2004)334 -344 TIPP 09 Tsukuba R&D: Weizmann/Coimbra/Aveiro VISIBLE-SENSITIVE GAS-PMs A. Breskin
Reverse-biased MHSP (R-MHSP) concept Ions are trapped by negatively biased cathode strips Reversed-MHSP (R-MHSP) Strips: collect ions Can trap only ions from successive stages Roth, NIM A 535 (2004) 330 Breskin NIM A 553 (2005) 46 Veloso NIM A 548 (2005) 375 TIPP 09 Tsukuba Flipped-Reversed-MHSP (F-R-MHSP) Can trap its own ions Lyashenko JINST (2006) 1 P 10004 Lyashenko JINST (2007) 2 P 08004 VISIBLE-SENSITIVE GAS-PMs A. Breskin
BEST ION BLOCKING: “COMPOSITE” CASCADED MULTIPLIERS: 1 st R-MHSP or F-R-MHSPion defocusing (no gain!) : Mid GEMs: gain Last MHSP: extra gain & ion blocking IBF=3*10 -4 IBF measured with 100% e-collection efficiency 5 IBF=3*10 -4 @ Gain=10 100 times lower than 3 GEMs Lyashenko 2007 JINST 2 P 08004 TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
New ideas for ion blocking NEW! “COBRA”: GEM-LIKE PATTERNED ION-SUPPRESSING ELECTRODES IBF=3*10 -6 Gain=105 IBF 1000 times lower than with GEMs; best results ever achieved But: 20% photoelectron collection efficiency… TRYING TO IMPROVE! TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
Visible-sensitive GPM Test detector setup UHV compatible materials Bi-alkali photocathode Sealed detector GEM/MHSP cascaded multiplier TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
UHV setup for photocathode/detector investigations • Multi-alkali photocathode production (QE 20 -40% @ 360 -420 nm in vacuum for semi-transparent PC) • Hot Indium sealing to package @130 -150ºC M. Balcerzyk et al. , IEEE TNS Vol. 50 no. 4 (2003) 847 D. Moerman, Ph. D Thesis 2005 JINST TH 004 TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
Typical QE of bi-alkali PC produced in our lab Lyashenko et al, in preparation Na-K-Sb K-Cs-Sb vacuum K-Sb -Cs PC ageing in avalanche mode • 20% QE drop @ 2 μC/mm 2 ion charge on photocathode: • only ~ 4 x faster drop compared to thin ST Cs. I (~8 μC/mm 2) Real conditions: gain=105; IBF=3*10 -4. • 20% QE drop 46 years @ 5 k. Hz/mm 2 ph. • same conditions with a MWPC (IBF=1) 3000 times shorter lifetime: ~5 days! Breskin NIM A 553 (2005) 46 TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
Continuous operation of F-R-MHSP/GEM/MHSP with K-Cs- photocathode Sb K-Cs. Sb 105 Cs. I Gain ~105 at full photoelectron collection efficiency First evidence of continuous high gain operation of visible-sensitive GPM TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
Visible-sensitive GPM features 100 photoelectrons 19 ns Single photon sensitivity No ion-feedback Fast ns pulses Lyashenko et al, JINST, in preparation TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
photocathode stability inside UHV preparation chamber gas fresh PC after 14 hours of operation PC is stable in gas in the large vacuum chamber Expected even better stability for sealed devices Kapton glass? Ceramic? Other? gas Rate: 12 k. Hz/mm 2 photons Gain: 105 Total anode charge ~125μC Lyashenko et al, JINST, in preparation VISIBLE-SENSITIVE GAS-PMs TIPP 09 Tsukuba A. Breskin
BACKSCATTERING IN GAS: EFFECTIVE QE QE eff = QE x transmission (e- extraction efficiency into gas) hn GAS Back-scattering PC transmission T R A N S M I S S I O N Cs. I Breskin, NIM A 483 (2002) 670 TIPP 09 Tsukuba T R A N S M I S S I O N Noble gases Cs. I Divergence due to scintillation Dashed-lines are simulation Coelho, NIMA 581(2007)190 VISIBLE-SENSITIVE GAS-PMs A. Breskin
Photoelectron transmission from K-Cs-Sb as a function of E-field & photon wavelengths QE eff = QE x transmission (e- extraction efficiency into gas) 700 Torr Methane NEW 700 Torr Ar/CH 4 (95/5) Higher effective QE at longer WL’s Lyashenko et al, in preparation TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
Summary Cascaded Patterned Hole Multipliers (MHSP/GEM) • RECORD in ion blocking in gaseous detectors, crucial in. GPMs • IBF~3 10 -4 with full photoelectron collection efficiency! • Further improvements in progress (other patterned electrodes) 5 • NEW : Stable visible-sensitive GPM DC-mode operation at 10 Photocathodes • “Reasonable” effective QE in 1 bar gas(18% @ 400 nm can be ); improved (gas/geometry ) • Potential applications • Atmospheric-pressure large-area photon detectors! • Potential applications in Particle Physics, Astroparticle, Medical, NDT, etc • Suitable for cryogenic operation (UV GPMs OK) SCIENTIFICALLY FEASABLE BUT: INDUSTRIAL PROJECT! TIPP 09 Tsukuba VISIBLE-SENSITIVE GAS-PMs A. Breskin
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